The invention relates generally to ultrasonic imaging methods and, more particularly, to improved near surface resolution for phased array ultrasonic inspection of industrial components.
Phased array imaging ultrasound systems are a promising tool for industrial inspections. However, conventional ultrasonic inspection methods exhibit poor near surface resolution for certain inspection configurations. In particular, it is often desirable to perform an ultrasonic inspection where a transducer is located in close proximity to the test object (such as a component or structure, collectively termed xe2x80x9ccomponentxe2x80x9d herein), in order to focus the ultrasound within the test object. However, industrial components, such as forgings, produce a strong reflection of the ultrasound from the surface of the component. The corresponding xe2x80x9cinterface signalxe2x80x9d has a relatively long duration, reducing the ability to detect defects near the surface of the component. FIG. 1 illustrates the conventional transmit/receive pattern for inspection of a component using phased array ultrasound. The corresponding predicted interface signal is shown in FIG. 2. Because of the relatively long interface signal, the signals that correspond to defects near the surface of the component are difficult to identify and characterize, decreasing the near surface resolution of the phased array ultrasonic inspection.
This near surface resolution issue for ultrasonic inspections has been addressed in different ways. One solution is to perform conventional ultrasonic inspection using a fixed geometry transducer instead of a phased array system. By xe2x80x9cfixed geometry,xe2x80x9d it is meant that the transducer has fixed focal properties. The transducer is scanned over the surface of the component several times along a predefined path (raster, circumferential, etc.), with each scan being performed at a different distance from the surface of the component. By adjusting the separation between the transducer and the component surface, each successive scan moves the focus of the scan further into the component. The interrogation gates used to monitor the signal from the component are moved accordingly to inspect the component at various depths. Although this method permits near surface resolution of defects, it is time consuming because it involves repeated inspections of the component.
Another solution is to inspect the industrial component, for example a forging, using the conventional phased array inspection technique described above with reference to FIG. 1. To compensate for the poor near surface resolution, the forging is made slightly larger than the desired final size. After the inspection, the forging is machined down to the desired size. Removal of the outer portion of the material renders the poor near surface resolution less important. However, this method is expensive as it involves using excess material for the forgings and extra machining steps.
Accordingly, it would be desirable to develop an ultrasonic inspection method for industrial applications, such as the inspection of aircraft engine forgings, that provides improved near surface resolution, without requiring the use of repeated scans at various distances from the surface of the test object.
Briefly, in accordance with one embodiment of the present invention, an ultrasonic inspection method includes exciting a first set of transducers in an array to introduce ultrasonic energy into a component, generating a number of echo signals using a second set of transducers in the array as receive elements, and processing the echo signals. The first and second sets of transducers are exclusive of one another, and the first and second sets of transducers are interleaved.